A wind turbine is a device that converts the wind's kinetic energy into electrical power.
Wind turbines are manufactured in a wide range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming an increasingly important source of intermittent renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels.
Wind turbines were used in Persia (present-day Iran) about 500–900 A.D. The windwheel of Hero of Alexandria marks one of the first known instances of wind powering a machine in history. However, the first known practical wind turbines were built in Sistan, an Eastern province of Iran, from the 7th century. These "Panemone" were vertical axle wind turbines, which had long vertical drive shafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these wind turbines were used to grind grain or draw up water, and were used in the gristmilling and sugarcane industries.
Wind turbines first appeared in Europe during the Middle Ages. The first historical records of their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch wind turbines were in use to drain areas of the Rhine delta. Advanced wind mills were described by Croatian inventor Fausto Veranzio. In his book Machinae Novae (1595) he described vertical axis wind turbines with curved or V-shaped blades.